Depends on how you define neutral. Or what you accept as neutral as defined by another.
My reference to "tube sound" acknowledged that there was a common, and limited, notion of what tubes provide. Not so.
If there was a true neutral device or chain, that is to say natural and realistic, we would all know about it and be convinced.
Personally, I am referencing neutral/natural/realistic back to live acoustic performance. Not saying it should be the same for everyone.
Solid state, tubes, vinyl, CD, Hi/LoRes files, DAC, COAX, USB, amp topologies, discrete/IC, etc, it all has some effect, be it subtraction, addition, distortion, or imbalance.
I think the assumption you are putting forth is that true, actual neutral components do exist and are ideally designed.
Wish it were so simple, we would all spend a lot less time and money.